BACKGROUND: Diet
directly influences systemic arterial hypertension (SAH), which is one of the
main risk factors for cardiovascular disease.OBJECTIVE: To associate hypertension
with dietary factors in adults clinically selected for a change-of-lifestyle
program.METHODS: Cross-sectional
study comprising 335 individuals, aged between 44 and 65 years, clinically
selected for a change-of-lifestyle program. We evaluated anthropometric data
(BMI, %body fat and waist circumference), biochemical components (plasma
glucose, triglycerides, total cholesterol, HDL-C and LDL-c) and diet, through
the 24-hour recall method. The quality of the diet was assessed by the Healthy
Eating Index. Blood pressure was measured according to the V Brazilian
Guidelines on Hypertension and classified according to NCEP-ATPIII. Logistic
regression was performed to determine the likelihood of changes in SBP and DBP
according to dietary intake. The level of significance was set at p <0.05.RESULTS: There was a positive
correlation between diastolic blood pressure and sugar and cholesterol intake,
and a negative one with intake of fiber, portions of oil and fats and diet
quality. Dietary variety with ≥ 8 food items showed a protective effect
for alterations in systolic blood pressure, OR = 0.361 (0.148 to 0.878).CONCLUSION: A greater
dietary variety had a protective effect on the systolic blood pressure.

Systemic arterial
hypertension (SAH) is a major risk factor for cardiovascular mortality, being
related to the increase of its incidence1,2. It has a greater
influence on the risk of cardiovascular disease than smoking,
hypercholesterolemia, hyperglycemia and obesity3.

According to population
studies, the prevalence of hypertension in Brazil varies from 25.2% to 41.1%4-6,
being more prevalent in women, especially after menopause7. The most
recent Basic Data Indicators (BDI) survey shows that the prevalence of
hypertension in the Brazilian population is 23.9% in adults, and when
considered by gender, 21% of men and 26.3% of women have the disease8.
SAH has high medical and socioeconomic costs arising mainly from its
complications, such as cerebrovascular disease, coronary artery disease, heart
failure, chronic renal failure and lower extremity vascular disease2.

Among the most
important associated risk factors, some are considered not modifiable such as
age, gender, ethnicity, socioeconomic factors and genetics. Among the
modifiable ones, the inadequate lifestyle is related to higher prevalence of
hypertension and reduced protection against the disease9. Therefore,
a key component for the prevention and treatment of hypertension is the change
in lifestyle, such as adopting a low-calorie diet, weight reduction, physical
activity, decrease alcohol and/or salt intake2, which is the most
effective and less costly way in terms of public health10.

The beneficial effects
of a healthy diet (rich in fruits and vegetables, low on fat) on the behavior
of blood pressure are well known11. Among the nutritional factors
that are associated with high prevalence of hypertension are the high
consumption of alcohol and sodium and excess weight. Recently, the consumption
of potassium, calcium and magnesium has also been associated, which would
attenuate the progressive increase in blood pressure with age12.

The Brazilian Society
of Hypertension, in its guidelines, has started to recommend the DASH (Dietary
Approaches to Stop Hypertension) diet in the non-pharmacological treatment of
hypertension 2. The DASH diet emphasizes increased consumption of
fruits, vegetables and low-fat dairy products, as well as whole grains,
poultry, fish and nuts, and reduced consumption of fats, red meat, sweets and
soft drinks. In a study carried out in patients with hypertension it has been
observed that DASH substantially reduced blood pressure (systolic: 5.5 mmHg) in
a period of two months, and, when combined with reduction in sodium intake,
there was an additional decrease in blood pressure (systolic: 8.9 mm Hg)13.

To our knowledge, no
national study has evaluated the influence of diet quality and consumption of
servings of the food pyramid on hypertension and/or alterations in systolic
(SBP) and diastolic blood pressure (DBP). Our group has shown the influence of
diet on some risk factors for cardiovascular disease14-16; however,
an association with hypertension has yet to be demonstrated. Accordingly, we
intend to study the association of diet on hypertension in adults clinically
selected for a change-of-lifestyle program.

Methods

Sample

A cross-sectional study
was carried out in a subgroup of individuals referred to a change-of-lifestyle
program, called "Move Pro-Health", in the city of Botucatu, state of São Paulo,
Brazil, from 2004 to 2008. Individuals were voluntarily recruited for the study
(convenience sample).

We evaluated 335
individuals, with or without systemic hypertension of both sexes (76.4% women),
aged between 44 and 65, selected for the change-of-lifestyle program.

All subjects signed an
informed consent form, which, together with the project, was approved by the
Ethics in Research Committee (protocol # 3271-2009) from Faculdade de Medicina
de Botucatu (FMB - UNESP).

The anthropometric assessment consisted of measurements
of body weight and height, according to the procedures described by Heyward and
Stolarczyk19, with subsequent calculation of Body Mass Index (BMI).
BMI was classified according to the World Health Organization20.

The Abdominal Circumference (AC) was measured using an
inextensible, inelastic, measuring tape and the measurement was performed at
midpoint between the lower margin of the last palpable rib and the iliac crest18.

The calculation of body
composition, body fat percentage (BF%) and Fat Free Mass (FFM) was carried out
by bioelectrical impedance (BIA) in a BiodynamicsÒ device (model
450, USA). Based on the resistance in ohms obtained by BIA and the calculation
of BMI, the equation of Segal et al. was applied to obtain the fat-free mass21.
Based on the values ​​of FFM, we estimated the Absolute Fat Mass
(AFM) by subtracting the body weight minus FFM and calculating the % BF.

Dietary Intake Assessment

Dietary intake was
assessed by nutritional history with the 24-hour recall method. The recall was
applied from Tuesday to Friday and the data related to the weekend were not
collected. Dietary data were in household measures and were converted to grams
and milliliters to enable chemical analysis of food consumption. Culinary preparations
made ​​with more than one food group had their ingredients
distinguished and classified in their respective groups, a procedure that
follows the adapted Brazilian Food Pyramid Guide recommendations22.

Subsequently, the data
were processed using the nutritional analysis software NutWin (2002), release
1.523. The quality of the diet was assessed by the Healthy Eating
Index (HEI)24, based on Adapted Brazilian Food Pyramid22.

HEI is a dietary
analysis method used to determine the individual's quality of diet. We
considered the eight food groups of the food pyramid, the percentage of total
fat, saturated fat, amount of dietary cholesterol and dietary variety for the
score. The variety of diet was defined as the amount of different food items
present in the diet.

Clinical assessment of blood pressure

We evaluated the
systolic and diastolic blood pressure of subjects in the sitting position,
according to the procedures described by the VI Brazilian Guidelines on
Arterial Hypertension2, with cuffs of adequate size for arm
circumference, respecting the width / length ratio of 1:2, the width on the
rubber cuff that must correspond to 40% of arm circumference, and its length,
of at least 80%. The time interval between blood pressure measurements was 1-2
minutes. The subjects were diagnosed as having hypertension according to "The
Adult Treatment Panel III of the National Cholesterol Education Program"
(NCEP-ATP III)18.

Statistical Analysis

The tests were
performed using SAS software release 9.1 and STATISTICA 6.0. Data were
presented as mean ± SD. For comparison of individuals with or without
hypertension, the t test was
used for continuous variables.. Normality of the sample was tested through the
Shapiro-Wilk test. Pearson's partial correlation was used to correlate the
dietary variables with systolic and diastolic blood pressure, adjusted for sex,
age, total caloric intake (TCI), and BMI. A linear regression analysis was
performed with 95% confidence interval (95%CI) to observe the odds ratio of the
studied individuals to present hypertension and alterations in SBP and DBP
according to dietary intake. Data were adjusted for sex, age, BMI, and TCI. The
results were discussed based on the significance level of p <0.05.

Results

It was observed that
individuals with hypertension had higher BMI, %BF and WC. There was no
significant difference between groups when dietary parameters were assessed.
Regarding the biochemical data, the group of hypertensive patients had higher
plasma concentrations of fasting glucose, total cholesterol, LDL-C and
triglycerides when compared to the nonhypertensive group (Table 1).

Table 2 shows
Pearson's correlation between the food groups and the values ​​of
SBP and DBP. There was a positive correlation between DBP and the consumption
of cholesterol and sugar, and a negative one with the consumption of fibers,
servings of oil/fats and HEI.

According to Table 3,
a dietary variety ≥ 8 food items showed a protective effect for
alterations in SBP. There was no association between diet and hypertension and
DBP.

To explain the inverse
relationship between dietary variety and SBP, a correlation was performed
between diet variety with all food components in order to characterize the
consumption of individuals who had more varied diets. A positive correlation
was observed between dietary variety with intake of vegetables (r = 0.34, p
<0.05), fruit (r = 0.32, p <0.05), fibers (r = 0.22, p <0.05), dairy
products (r = 0.20, p <0.05) and HEI (r = 0.20, p <0.05) and a negative
one for legume consumption (r = -0.11; p <0.05), meats (r = -0.15, p
<0.05) and cereals (r = -0.19, p <0.05). There was no significant
correlation for intake of macronutrients, servings of oil/fats and sugar (data
not shown).

Discussion

The main result of
this study was that dietary variety (food items ≥ 8) offered a protective
effect for alterations in SBP regardless of gender, age, BMI, and TCI.
Furthermore, we observed a positive correlation between dietary variety and
food sources of potassium, calcium and fibers (vegetables, fruit, dairy products)
and a negative one with foods high in saturated fat, sodium and refined
carbohydrates (meat and % of carbohydrate).

The consumption of
potassium, calcium and magnesium has been associated with attenuation of the
progressive increase in blood pressure levels12. Potassium is
responsible for the reduction in intracellular sodium through the
sodium-potassium pump and induces the decrease in blood pressure (BP) by
increasing the natriuresis, reducing renin and norepinephrine and increasing
prostaglandin secretion. Calcium helps regulate the heartbeat and reduces
sodium levels when in high concentrations and magnesium inhibits the
contraction of vascular smooth muscle and may play a role in regulating BP as a
vasodilator25,26.

A study carried out
recently in Japan investigated the associations of consumption of fruit,
vegetables and their micronutrients with a reduced risk of SAH. The high
consumption of fruit and vegetables was associated with a lower risk of
developing hypertension, suggesting that the decrease in blood pressure was due
to the presence of potassium and vitamin C in the foods27. A study
with Australian adolescents showed that the consumption of fruit, vegetables,
grains and fish was inversely associated with DBP28.

No direct effect of
fruit and vegetable consumption was observed in our study, probably due to the
fact that both hypertensive and nonhypertensive patients showed low consumption
of this type food; moreover, there was no difference regarding the consumption
of these food groups between the groups.

The consumption of
fibers was negatively correlated with the decrease in BP, albeit weakly. This
fact can also be explained by the low fiber consumption in both groups. It is
known that individuals with high intake of dietary fiber may have significantly
lower risk for developing coronary heart disease, infarction, hypertension,
diabetes and obesity29,30.

We observed a positive
correlation between sugar consumption and DBP. Inadequate consumption of this
type of food is associated with increased insulin production, and may have a
direct effect on the increase in renal reabsorption of sodium and thus,
increase BP31. Moreover, insulin resistance and hyperinsulinemia may
play a role in the pathogenesis of hypertension associated with obesity, due to
the increase in inflammatory markers32,33. Hyperinsulinemia causes
increased activity of the sympathetic nervous system and tubular reabsorption
of sodium, actions that contribute to the increase in BP34-36.

Higher BMI, %BF and WC
were observed among individuals with hypertension, which was expected37.
Visceral fat can mediate the increase in blood pressure by reducing the
natriuresis. The higher sodium retention would be caused by the activation of
the renin-angiotensin system, activation of the sympathetic nervous system and
also by changes in intrarenal hemodynamics, consequent to the compression of
the renal medulla38. This shows the importance of adjusting the data
for adiposity (BMI) when we analyze the influence of diet on hypertension,
because then, these effects can be neutralized.

It was observed that
hypertensive individuals showed higher plasma glucose, glycemia, total
cholesterol, triglycerides and LDL-C levels, which increases the risk of
cardiovascular diseases30. According to Schaan et al39,
individuals with some degree of abnormal glucose homeostasis had a higher
prevalence of hypertension.

Study
limitations

This was a
cross-sectional study, and, therefore, the cause-effect mechanisms cannot be
defined. Secondly, 24-hour recall was conducted in a single a day, which may
not accurately reflect the habits of the evaluated individuals. Moreover, the
consumption of sodium and alcohol was not evaluated, which may influence blood
pressure.

Conclusion

The present study
showed that the greater the dietary variety (eight or more different types of
food) offered a protective effect for alterations in SBP. The other dietary
variables studied were not significantly associated with BP.